i going to create print media (letterhead, business cards, flyers, brochures...) with Illustrator and photoshop and i would like to know if there is a plug-in to visualize / render the work in 3D as if it was already printed on paper ?

Illustrator and Photoshop have capabilities to provide depth/perspective/warp. Even before these features were added in recent years, you could skew/distort 2D forms to give the appearance of 3 dimensions.

It sounds like you don't need to do any 3D transformation, just use color and texture so it looks like you've printed on 100% cotton paper or heavy card stock. You can play with the textures in Photoshop to get the effect you're looking for.